| Electric vehicles,which can achieve clean and pollution-free emissions,are the development goal for the future transportation.The hybrid energy sources system of the electric vehicles is composed of a battery bank and a super capacitor bank,where the high specific energy battery is used as the power battery to establish the bus voltage through a bidirectional dc-dc converter and provide the steady-state and low-frequency power to the bus,and the high specific power super capacitor provide transient and high-frequency power to the bus through a bidirectional dc-dc converter.The hybrid energy sources work coordinately,servicing the required bidirectional power for the bus.Therefore,it is of great significance to study the high-efficiency and wide-voltage-gain bidirectional dc-dc converter and the coordinate operation strategy of the hybrid energy sources system.In order to match the wide-range voltage of the super capacitor caused by the charging and discharging,a stepped and modular bidirectional dc-dc converter with wide voltage gain is proposed.The converter adopts switched-capacitor structure and interleaved parallel form.It has the advantage of low voltage stresses and low current ripple of the low voltage side and easy to extend.It can also dynamically match a wide-range voltage of super capacitor with a constant bus voltage.In addition,in order to reduce the large surge current impact on the power battery generated by the sudden change of load,the paper adopts the power frequency-division operation control strategy of the hybrid energy sources system to realize that the power battery absorbs and releases the steady-state and low-frequency power,and the super capacitor swallows and spits the transient high-frequency power,which prolongs the life of the power battery.At the same time,the converter connected to the power battery operates as voltage source to establish a stable bus voltage while the converter connected to the super capacitor operates as current source.Finally,a multi-mode operation control strategy based on the super capacitor’s voltage range is proposed to ensure the long-term stable operation of the hybrid energy sources system.The control strategy is divided into seven modes,including bus power absorption state and bus power feedback state.It ensures that the super capacitor will not be in the limit voltage range caused by frequent charging and discharging,and the super capacitor can operate under the normal voltage range continuously. |
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